Farnesol is a natural 15-carbon organic compound which is an acyclic sesquiterpenealcohol. Under standard conditions, it is a colorless liquid. It is hydrophobic, and thus insoluble in water, but miscible with oils. Farnesol is produced from 5-carbon isoprene compounds in both plants and animals. Phosphate activated derivatives of farnesol are the building blocks of most, and possibly all, acyclic sesquiterpenoids. These compounds are doubled to form 30-carbon squalene, which in turn is the precursors for steroids in plants, animals, and fungi. As such, farnesol and its derivatives are important starting compounds for both natural and artificial organic synthesis.
Uses
Farnesol is present in many essential oils such as citronella, neroli, cyclamen, lemon grass, tuberose, rose, musk, balsam and tolu. It is used in perfumery to emphasize the odors of sweet floral perfumes. Its method of action for enhancing perfume scent is as a co-solvent that regulates the volatility of the odorants. It is especially used in lilac perfumes. Farnesol is a natural pesticide for mites and is a pheromone for several other insects. In a 1994 report released by five top cigarette companies, farnesol was listed as one of 599 additives to cigarettes. It is a flavoring ingredient.
Farnesol is produced from isoprene compounds in both plants and animals. When geranyl pyrophosphate reacts with isopentenyl pyrophosphate, the result is the 15-carbon farnesyl pyrophosphate, which is an intermediate in the biosynthesis of sesquiterpenes such as farnesene. Oxidation can then provide sesquiterpenoids such as farnesol.
History of the name
Farnesol is found in a flower extract with a long history of use in perfumery. The pure substance farnesol was named after the Farnese acacia tree, since the flowers from the tree were the commercial source of the floral essence in which the chemical was identified. This particular acacia species, in turn, is named after Cardinal Odoardo Farnese of the notable Italian Farnese family which maintained some of the first private Europeanbotanical gardens in the Farnese Gardens in Rome. The addition of the -ol ending results from it being chemically an alcohol. The plant itself was brought to the Farnese gardens from the Caribbean and Central America, where it originates.
Health effects
Farnesol has been suggested to function as a chemopreventative and anti-tumor agent. Farnesol is used as a deodorant in cosmetic products because of its anti-bacterialactivity. Farnesol is subject to restrictions on its use in perfumery as some people may become sensitised to it, however the evidence that farnesol can cause an allergic reaction in humans is disputed. In a study, researchers found in a tissue culture that Balsam of Peru and farnesol were able to bind to CD1a molecules on the surface of Langerhans cells and active T cells. However, researcher de Jong notes that, "Our work shows how these chemicals can activate T cells in tissue culture, but we have to be cautious about claiming that this is definitively how it works in allergic patients. The study does pave the way for follow up studies to confirm the mechanism in allergic patients and design inhibitors of the response." Despite this warning, some pop-science has taken the preliminary findings of this study to be conclusive evidence that farnesol causes an immunological response through this mechanism. Even though the study did not test this on functional human skin.
